Variable voltage transformer



Dec. 15; 1964 w. MASTER I 3,161,842

. VARIABLE VOLTAGE TRANSFORMER Filed June 19, 1962 INVENTOR. h HARE/V M45 7-5? ATTORNEYS United States Patent 3,161,842 VARIABLE VOLTAGE TRANSFORMER Warren Master, Rutherford, N.J., assignor to Tang-Sol Electric Inc, a corporation of Delaware Filed .lune 19, 1962, Ser. No. 203,566 11 Claims. (Ql. 336-45) This invention relates to a variable voltage transformer which receives a constant input voltage from an alternating current power supply and delivers a voltage which may be varied by manual means. The voltage is varied by the adjustment of a short-circuiting coil. The invention has particular reference to an annular magnetic core having a magnetic shunt for diverting part of the magnetic flux generated by current in the windings.

Variable voltage transformers are quite common and are in wide use in laboratories for testing and any other applications where an adjustable voltage is required. These transformers all have contacts and produce their voltage variations due to a sliding contact which sequentially connects with a series of wires or contact terminals. This type of transformer obviously is subject to sparking when the contact arm is moved and is subject to heating where the electrical connection is made. The present invention has no contacts and during the voltage adjustment, neither the primary circuit nor the secondary circuit is opened. There is no fire hazard and the rise and fall of the voltage is smooth and is not made in steps.

One of the objects of the invention is to provide an improved variable voltage transformer which avoids one or more of the disadvantages and limitations of prior art arrangements.

Another object of the invention is to provide a variable voltage transformer without any switching arrangements.

Another object of the invention is to provide a variable transformer with a smooth adjustable voltage characteristic.

Another object of the invention is to increase the efficiency of variable voltage transformers by providing a core with a minimum airgap length.

Another object of the invention is to reduce the heat generated in a variable voltage transformer by providing an efficient magnetic system having low reluctance.

Another object of the invention is to reduce the fire and explosion hazard when operated in locations where flammable fluids and gases are present.

The transformer includes a core of ferromagnetic material having an annular main magnetic path. A plurality of windings are positioned on the core with terminals for connection to a source of alternating current power and a load circuit. The core is also provided with at least one shunt for diverting a portion of the flux from the main path. A rotatable shortcircuited winding encloses the annular core and is movable exterior to all of the plural windings. The rotatable winding is supported so that it may be adjusted by an operator.

For a better understanding of the present invention, together with other and further objects thereof, reference is made tothe following description taken in connection with the accompanying drawing.

FIG. 1 is a schematic diagram of the core and windings showing one arrangement for producing a wide variation in output voltage.

FIG. 2 is a side view of the transformer showing the short-circuiting coil secured to a knob for manual movement.

FIG. 3 is a cross sectional view of the transformer shown in FIG. 1 taken generally along line 3-3 of that figure.

FIG. 4 is a schematic diagram similar to FIG. 1 but showing a core having two magnetic shunt paths.

3,161,842 Patented Dec. 15, 1564 FIG. 5 is a simplified diagram of connections for explaining the operation of the transformer.

Referring now to the drawing, the transformer includes an annular core 10 which may be of a plurality of laminations of transformer iron. The core is provided with a shunt member 11 which extends from a portion of the annular core across the center of the transformer and terminates at short distance from the other side of the annular portion. As shown in FIG. 1, three windings 12, 13, and 14 are wound on the annular portion of the core. These same windings are shown in FIG. 5. Windings 12 and 13 are arranged so that current through them aids in producing magnetic flux. Coil 14 is wound in a reverse direction so that it produces magnetic flux which opposes the flux produced by the other two windings.

A movable short-circuited winding 15 also surrounds the annular portion of the core but is wound on a base 16 which has clearance over the other coils and may be moved over them for most of the extent of the annular portion. The short-circuited coil 15 may be made with a single turn or it may have a number of turns with the two ends connected together. The short-circuited coil acts as a barrier to prevent the passage of magnetic flux in that portion of the core which it surrounds. The base 16 which supports the short-circuited winding 15 is secured to an arm 17. Arm 17 is rotatably mounted on a shaft 18 pivoted at the center of the core. A knob 20 may be used to adjust the position of the short-circuited winding but any other means of adjustment may be employed.

The windings may be positioned on the core in a number of patterns and the input and output connections to the transformer are subject to a wide variation of connecting arrangements, depending upon the range of the variable voltage desired and the maximum value of the output voltage. In the circuit shown in FIGS. 1 and 5, input terminals 21, 22, are connected respectively to a mid-point 23 on winding 12 ad the upper end of winding 13. Output terminals 24 and '25 are shown connected respectively to the lower end of winding 12 and one end of winding 14. This particular arrangement of connections provides the greatest range of output voltages and is capable of producing a zero output voltage or a voltage which is equal to percent of the input voltage.

The transformer shown in FIG. 4 illustrates an alternate type of core which may be used. In this arrangement, the annular portion 10 supports all the windings 26, 27, 28, but the shunt portion is shaped like a Y and thereby provides two airgaps 30 and 31. When the short-circuiting coil 15 is moved to a position where it encloses winding 28, the flux through that portion of the core is reduced to a very small value but the other two Win-dings 26 and 27 still produce flux which travels in paths indicated by arrows 32 and 33. When the short-circuiting winding is moved to a position where it encloses winding 27, the flux through that portion of the core is practically cut off but the flux produced by windings 26 and 23 travels in paths as indicated by arrows 33 and 34. In a similar manner, winding 15 may be moved over winding 26 and similar results produced. It is obvious that various combinations of windings can be designed for such a core arrangement to produce many varied output voltage characteristics. Perferably the spacing between adjacent windings on the core is equal to at least one-tenth of the peripheral distance of the annular core and the length of the short-circuited winding is less than such spacing.

In order to explain the operation of the transformer shown in FIG. 1, a simplified diagram is shown in FIG. 5, this diagram having all the windings and the same connections as the diagram shown in FIG. 1. When 3 winding 15 is moved so that it encloses winding 14, the impedance through this winding and its magnetic flux is reduced to a very low value and the output voltage is substantially equal to the voltage between terminal 24 and tap 35. This voltage can be made more than the input voltage by a proper selection of turns. When the short-circuiting winding is moved to enclose winding 12, the impedance and flux produced by this winding are reduced to a very low value and the output voltage is then the combination of voltages produced by windings 13 and 14. These two windings, however, are designed to buck each other and by proper selection of turns the voltage across terminals 24 and 25 may be made equal to zero. Positioning the short-circuited winding 15 in intermediate positions produces intermediate results and a smooth voltage variation, without incremental steps, is available at the output terminals.

It is obvious from the above description that a magnetic shunt must be provided to give a path for one portion of the transformer while the other portion is being blocked.

The foregoing disclosure and drawings are merely illustrative of the principles of this invention and are not to be interpreted in a limiting sense. The only limitations are to be determined from the scope of the appended claims.

I claim:

1. A variable voltage transformer comprising: a core of ferromagnetic material having an annular main magnetic portion, a plurality of windings on said annular portion with terminals for connection to a source of alternating current power and a load circuit, said core having at least one magnetic shunt for diverting a part of the flux from the main portion, a rotatable shortcircuited winding enclosing said annular core and movable exterior to said plural windings, and means for supporting the short-circuited winding to move it in a circular path.

2. A variable voltage transformer for varying the voltage across a pair of output terminals comprising: a core of ferromagnetic material having an annular closed main magnetic portion, a plurality of windings on said annular portion with connections to terminals for receiving power from an alternating current supply and for delivering power to a connected load, said core having at least one magnetic shunt for diverting magnetic flux from the main portion, a rotatable short-circuited winding enclosing said annular core and movable exterior to all of said plural windings for substantially the entire extent of the main magnetic portion, and pivoted means for supporting the short-circuited winding to move it in a circular path.

3. A variable voltage transformer as claimed in claim 2 wherein said magnetic shunt extends from one portion of the main annular path to a position adjacent the opposite portion.

4. A variable voltage transformer for varying the voltage across a pair of output terminals comprising: a core of ferromagnetic material having an annular main magnetic portion, at least two windings on said annular portion with connections to input terminals for receiving alternating current power and for delivering power to a connected load, one of said windings connected so that current through the winding produces magnetic flux which opposes the flux produced by the current in the other windings, said core having at least one magnetic shunt for diverting magnetic flux from the main portion, a rotatable short-oircuited winding enclosing said annular core and movable exterior to all of said annular windings, and means for supporting the short-circuited winding to move it in a circular path.

5. A variable voltage transformer as claimed in claim 4 wherein said means for supporting the short-circuited winding includes a pivoted arm and a knob for manual adjustment.

6. A variable voltage transformer as claimed in claim 4 wherein one of said two windings is on one part of the annular core and the other of said windings is on another part of the core, separated from the first portion by an airgap between the annular core and said magnetic shunt.

7. A variable voltage transformer as claimed in claim 4 wherein said core has two magnetic shunts, both of said shunts joined at one end where the shunts join the annular magnetic position, and each of said shunts terminated by an airgap at its other end.

8. A variable voltage transformer as claimed in claim 7 wherein a winding is positioned on said annular core between said two airgaps.

9. A variable voltage autotransformer for varying the voltage across a pair of output terminals comprising: a

a laminated core of ferromagnetic material having an annular magnetic portion; at least two windings on said annular portion, each separated from the other by a distance equal to at least one-tenth of the peripheral distance of the annular portion; terminal connections for receiving alternating current power from a source of supply and for delivering power to a connected load; one of said windings connected so that current through the winding produces magnetic flux which opposes the flux produced by the current in the other windings; said core having at least one magnetic shunt for diverting magnetic flux from the main portion and by passing at least one of said windings, said magneticshunt having a vairgap for increasing its magnetic reluctance; a rotatable short-circuited winding enclosing said annular core and movable exterior to all of said annular windings and pivot means for supporting the short-circuited winding to move it in a circular path.

10. A variable voltage transformer as claimed in claim 9 wherein said magnetic shunt is formed of ,larninations each of which is integral with one of the laminations forming the annular portion of the core.

11. A variable voltage transformer as claimed in claim 9 wherein said wshort-oircuited winding has .a length which .is less than one-tenth of the peripheral length of the annular magnetic portion.

References Cited in the file of this patent UNITED STATES PATENTS 400,515 Thomson Apr. 2, 1889 428,620 Lemp et 'al. May 27, 1890 440,640 Lemp Nov. 18, 1890 1,735,141 Sturner Nov. 12, 1929 2,905,912 Geiser i Sept. 22, 1959 

1. A VARIABLE VOLTAGE TRANSFORMER COMPRISING: A CORE OF FERROMAGNETIC MATERIAL HAVING AN ANNULAR MAIN MAGNETIC PORTION, A PLURALITY OF WINDINGS ON SAID ANNULAR PORTION WITH TERMINALS FOR CONNECTION TO A SOURCE OF ALTERNATING CURRENT POWER AND A LOAD CIRCUIT, SAID CORE HAVING AT LEAST ONE MAGNETIC SHUNT FOR DIVERTING A PART OF THE FLUX FROM THE MAIN PORTION, A ROTATABLE SHORTCIRCUITED WINDING ENCLOSING SAID ANNULAR CORE AND MOVABLE EXTERIOR TO SAID PLURAL WINDINGS, AND MEANS FOR SUPPORTING THE SHORT-CIRCUITED WINDING TO MOVE IT IN A CIRCULAR PATH. 